1. Field of the Invention
The present invention relates to an apparatus or system adapted to perform an abrasive machining operation using an abrasive tape.
2. Discussion of the Related Art
There is known an abrasive machining apparatus of a type wherein an abrasive tape and a workpiece are moved relative to each other while the abrasive tape is forced onto a desired portion of the surface of the workpiece to be machined, and wherein the abrasive tape is fed in its longitudinal direction. The term "abrasive tape" is interpreted to mean a strip-like member which consists of a flat substrate made of a fabric, paper, synthetic resin or other suitable material, and an abrading material, usually in the form of abrasive particles bonded to the surface of the substrate. The abrasive tape is fed before, after or during an abrasive machining process. The abrasive machining processes include a grinding process and a lapping process, for example.
One form of the known abrasive machining apparatus of the type indicated above will be described by reference to FIG. 21. This prior art apparatus of FIG. 21 is not completely identical with but is similar to an abrasive machining apparatus disclosed in JP-U-60-7952 (laid-open publication in 1985 of Japanese Utility Model Application).
To begin with, the prior art abrasive machining apparatus will be briefly described. The apparatus is adapted to grind the outer circumferential surface of a cylindrical workpiece W, such that a grinding operation takes place at predetermined two positions of the outer circumference of the workpiece W which are opposed to each other in a diametric direction of the workpiece. The abrasive machining apparatus uses a single abrasive tape T, which is forced simultaneously onto the outer circumferential surface of the workpiece W at the above-indicated two diametrically opposite grinding positions. In operation of the apparatus, the workpiece W is rotated about its axis, relative to the abrasive tape T, to thereby grind the workpiece W. In this apparatus, the abrasive tape T is held stationary during each abrasive machining or grinding cycle on the workpiece W, and is fed by a predetermined distance in the longitudinal direction after each grinding cycle, that is, before the next cycle is initiated, so that unused portions of the abrasive tape T are forced onto the predetermined portions of the workpiece W in the next grinding cycle.
Described in detail, the abrasive machining apparatus includes a pair of shoes 400 which are disposed on the opposite sides of the workpiece W and are opposed to each other in a diametric direction of the workpiece W, as shown in FIG. 21. These shoes 400 are attached to end portions of respective clamp arms 402 which are pivotable about an axis of a shaft 401. The other end portions of the two clamp arms 402 are connected by an air cylinder 403, which permits the two opposed shoes 400 to be moved toward and away from each other and the workpiece W.
The predetermined two grinding positions of the workpiece W at which the grinding operation by the abrasive tape T takes place are the two diametrically opposite circumferential positions of the workpiece W at which the two shoes 400 are opposed to each other diametrically of the workpiece. The abrasive tape T is fed generally from right to left as seen in FIG. 21 wherein the right-hand side portion of the apparatus is a tape incoming side while the left-hand side portion is a tape outgoing side. The abrasive tape T is threaded through the apparatus, that is, between the shoes 400 and the outer circumferential surface of the workpiece W. Explained more particularly, a roll of an unused length of the abrasive tape T is carried by a supply reel 404 which is rotatably disposed on the body of the apparatus. The unused portion of the abrasive tape T supplied from the supply reel 404 is threaded via the shoes 400 while being guided by a suitable number of guide rolls 406 and the used portion of the tape T is directed up to the outgoing side of the apparatus and eventually ejected into a tape tray 408 provided there.
The path along which the abrasive tape T is threaded will be described in detail. The leading end portion of the abrasive tape T supplied from the supply reel 404 is first passed along the outer surface of the clamp arm 402 on the tape incoming side of the apparatus, while being guided by some of the guide rolls 406 The leading end portion of the tape T is then passed along the inner surface of the shoe 400 on the tape incoming side. The tape T is not turned through 180.degree. around the workpiece W between the two shoes 400 but is turned around the guide roll 406 which is located between the workpiece W and the shaft 401 and between the two clamp arms 402 The tape T is then passed along the inner surface of the shoe 400 on the tape outgoing side of the apparatus, and along the outer surface of the clamp arm 402 on the tape outgoing side. The abrasive tape T thus threaded through the apparatus has respective portions which simultaneously contact the two diametrically opposite arcuate portions of the outer circumferential surface of the workpiece W. The tape has a non-contact portion between the two portions which contact the workpiece.
As described above, the abrasive tape T is threaded through the apparatus such that the tape T is not in contact with the two arcuate portions of the outer circumference of the workpiece W. This arrangement appears to be intended to permit easy and stable removal of the abrasive tape T away from the workpiece W upon installation and removal of the workpiece W on and from the abrasive machining apparatus, and to facilitate replacement of the tape T.
The present abrasive machining apparatus is adapted to feed the abrasive tape by a predetermined distance after termination of each grinding cycle, by rotating a pair of take-up rolls 410 which are geared with each other, so that a predetermined unused length of the tape T is supplied from the supply reel 404 toward the pair of shoes 400 and the corresponding used length of the tape T is ejected into the tape tray 408.
The prior art apparatus which has been described is of a workpiece rotation type adapted to perform a grinding operation by rotating the workpiece W relative to the abrasive tape T which is held stationary during the grinding operation. However, the relative movement of the workpiece W and the tape T may be effected by feeding the abrasive tape T continuously during the grinding operation while the workpiece W is held stationary.
The prior art abrasive machining apparatus has the following problems, irrespective of the type of relative movement between the workpiece and abrasive tape.
Generally, the abrasive tape used on the apparatus is replaced as needed by the operator of the apparatus. For instance, the replacement of the abrasive tape T is required when the machining surface of the tape T has become dull or "glazed", or when the tape is cut off for some reason or other during the operation of the apparatus.
In the known abrasive machining apparatus, however, the components such as the guide rolls and shoes associated with the replacement of the abrasive tape, that is, the components which define the path of the tape, are unremovably attached to the apparatus. Therefore, upon replacement of the used abrasive tape, the operator of the apparatus must remove the tape from the guide rolls, pass the new abrasive tape around the rolls, and make adjustments necessary to achieve correct threading of the new tape along the predetermined path through the apparatus. This operation is cumbersome and time-consuming, and makes it difficult to achieve abrasive machining operations with a sufficiently high efficiency. The apparatus suffers from this problem where the single abrasive tape is used for simultaneous grinding of two or more portions of the workpiece, as well as where the tape is used for grinding a single portion of the workpiece.
Thus, the known apparatus wherein the components defining the path of the abrasive tape are not removable suffers from low efficiency of replacement of the abrasive tape, irrespective of the type of relative movement between the abrasive tape and the workpiece, and irrespective of whether the abrasive tape is used to perform abrasive operation on one portion or a plurality of portions of the workpiece surface.
The abrasive machining apparatus shown in FIG. 21 uses one abrasive tape for performing simultaneous grinding operations at two grinding positions of the workpiece, as explained above. The abrasive tape is threaded in contact with one of the two diametrically opposite portions of the outer circumference of the workpiece while passing in one direction, and also in contact with the other circumferential portion of the workpiece while passing in the opposite direction. Thus, the threading path of the abrasive tape tends to be complicated, and increases the difficulty of replacement of the abrasive tape, leading to another problem, that is, an increased time required for replacing the abrasive tape.
The known apparatus of FIG. 21 has a further problem explained below.
The apparatus is of the workpiece rotation type adapted to perform abrasive machining operations by rotating the workpiece and to feed the abrasive tape by a predetermined distance after each machining cycle on the two portions of the workpiece. One of the two portions of the workpiece which is on the tape incoming side is necessarily contacted with an unused portion of the abrasive tape when the tape is fed. The other portion of the workpiece on the tape outgoing side must also be contacted with an unused portion of the tape. The portion of the tape used for the tape incoming side portion of the workpiece is fed between the two portions of the workpiece, as the non-contact portion indicated above. The used portion of the tape should not be used again for the tape outgoing side portion of the workpiece. Therefore, the tape should be fed by a distance corresponding to the length of the tape between the two portions of the workpiece, when the used portion of the tape has reached a point near the tape outgoing side of the workpiece. This feeding control of the tape is complicated, and a part of the tape cannot be used. If the tape is fed by a distance larger than the length of the tape between the two portions of the workpiece so that the tape outgoing side portion of the workpiece is necessarily contacted with the unused portion of the tape, a considerable part of the tape is wasted. Thus, the prior art apparatus suffers from wasting of the abrasive tape or requires a complicated control to feed the tape.